It is well known that mechanically rotating mirrors can redirect and steer optical beams. A fast steering mirror can be used to scan the beam while an adaptive optics element (e.g., a spatial light modulator) can be used to correct residual optical aberrations. See, e.g., U.S. Pat. No. 7,742,213 to Potsaid et al.; and B. Potsaid, L. I. Rivera, and J. T. Y. Wen, “Adaptive Scanning Optical Microscope (ASOM): large field of view and high resolution imaging using a MEMS deformable mirror—art. no. 646706,” MEMS Adaptive Optics 6467, 46706-46706 (2007), both incorporated herein by reference. U.S. Pat. No. 7,742,213 to Potsaid et al. discloses an imaging system that uses a steering mirror to select the field of view and an “adaptive optics element” to compensate for optical aberrations. The parallel stochastic gradient descent optimization algorithm was used in that patent to set the adaptive optics element and correct for system optical aberrations. The purpose is to optimize microscope image quality. The method of redirecting and steering optical beams, which utilizes a fast steering mirror, imposes significant weight and size restrictions on the device.
The use of spatial light modulators (“SLM”) to steer light beams by forming a blazed phase grating has been described in various references. See, e.g., U.S. Pat. No. 7,283,291 to Maram et al.; and B. Lofving et al., “Beam steering with two ferroelectric liquid-crystal spatial light modulators,” Opt Lett 23, 1541-1543 (1998), both incorporated herein by reference. Such blazed phase grating devices use a blaze period and pitch to achieve a desired deflection angle. No adaptive phase correction is performed with the SLM to correct for aberrations that may be present due to the optical elements in the system. For example, U.S. Pat. No. 7,283,291 to Maram et al. uses an SLM to perform beam steering. In that patent, a blazed phase grating is induced on the SLM to perform the beam steering function. Forcing a blazed grating onto the SLM prevents Maram et al. from using the SLM to correct for any optical aberrations caused by the optional static optical elements described in the patent. Therefore, the laser power in the desired direction is typically not optimized because wide-field of view optics generally cause optical aberrations. As another example, the “Beam steering with two ferroelectric liquid-crystal spatial light modulators” paper by Lofving et al. uses an SLM for beam steering, a second SLM to block out higher order beams and a lens to angularly amplify the steering field of regard. Since a lens is used to angularly amplify the transmitted lower order beam, the lens increased field of regard will typically have optical aberrations yet there is no apparent plan to compensate for them in this design. Methods that utilize the spatial light modulator as a steering device, but which do not correct for system aberrations impose tight tolerance and lens design requirements on the system's optical elements in order to maintain a tight, focused beam.